CBS has taken an early lead among the major networks in striking deals with advertisers to buy time during the new fall television season.

The broadcast networks are busy trying to sell the bulk of their prime-time ad spots in what is known the “upfront” market.

NBC, Fox and the new CW also are reported to be writing some smaller deals. Fox is owned by News Corp., the parent company of The Post.

CBS, home to hit shows “CSI” and “Without a Trace,” got an initial jump on rival ABC, a Disney-owned unit, which was expected to lead the pricing in this year’s upfront because of higher ratings.

While ABC could still wind up extracting the biggest rate hikes from advertisers, some media analysts wonder if its network has lost the upper hand.

The upfront negotiations got off to a slow start because ABC, along with the other networks, took the position that they should get paid more for ratings that include viewers who use TiVo and similar recording devices.

Advertisers and their media buyers balked at that stance, believing that while the recorders allow more viewers to watch shows, most end up skipping the ads.

ABC held out the longest before sending out a statement saying it would table the debate for now.

“ABC is probably lagging right now,” said one media buyer who is negotiating for a client in the upfront. “They had the firmest stance.”

Despite a ratings resurgence and hits such as “Lost” and “Grey’s Anatomy,” ABC still charges lower upfront rates than networks such as NBC, giving it some leverage to ask for increases.

Overall, the upfront pricing is murky. At least one media buyer said CBS is getting modest rate increases, from 2 to 4 percent, thanks to its relatively stable ratings and programming lineup. Other reports say CBS and the networks are writing deals at rates below last year’s.

A CBS spokesman would only confirm that the network has written some business. “We’re pleased with the way things are going,” said CBS’ Dana McClintock.

Last year, the broadcast upfront totaled about $9.1 billion. Most industry watchers predict the market will be flat or down this year, depending in part on how much fourth-ranked NBC declines after getting whacked in last year’s upfront.

“I think the market will be down,” said Jack Myers, a veteran media analyst who has tracked the upfront market for years. “The question is, ‘How down NBC will be.’ ”